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Re: [Qemu-block] [Qemu-devel] [PATCH 1/2] qemu-iotests: add _filter_qmp_

From: Eric Blake
Subject: Re: [Qemu-block] [Qemu-devel] [PATCH 1/2] qemu-iotests: add _filter_qmp_events() for filtering out QMP events
Date: Wed, 10 Feb 2016 15:14:35 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0

On 02/10/2016 11:52 AM, Sascha Silbe wrote:
> Dear Max,
> Max Reitz <address@hidden> writes:
>>> +# remove QMP events from output
>>> +_filter_qmp_events()
>>> +{
>>> +    sed -e '/^{\(.*, \)"event": ".*}$/ d'
>>> +}
>> There is a pretty good reason test 067 uses -qmp-pretty (as you yourself
>> say, the lines get pretty long otherwise, and if we have any change
>> within, the whole line needs to be changed).
> Additionally, it's a lot easier to read when indented properly,
> especially with the block info containing nested dicts.
>> Using the following ugly
>> piece of code here instead, we would still be able to use it:
>> tr '\n' '\t' \
>>   | sed -e
>> 's/{\s*"timestamp":\s*{[^}]*},\s*"event":[^,}]*\(,\s*"data":\s*{[^}]*}\)\?\s*}\s*//g'
>> \
>>   | tr '\t' '\n'
> Nice trick. Why didn't I come up with it? ;)

Mishandles any event whose data includes nested dicts.  But a little bit
more creativity can do it in two passes (the first modifies the stream
to mark the start of an event, the second then does multiline matching
to nuke the entire event):

tr '\n' '\t' |
  sed 's/^{\(\s*"timestamp":\s*{[^}]*},\s*"event":\)/{MARK\1/g' |
  tr '\t' '\n' |
  sed '/^{MARK/,/^}/d'

> It definitely is a bit ugly, though. We can't just drop the entire line
> (using "d") as the entire stream now is a single line. Matching
> parenthesis pairs is context sensitive, so we can't just use regular
> expressions to aggregate results into lines. And before I start
> implementing a JSON indenter in awk, I'd rather rewrite the whole test
> in Python. So if we stay with the shell test for now, we need something
> like your incantation above. It's not perfect, but good enough for now
> and I can't think of anything significantly simpler right now either.
> Will test your version and send a v2. Thanks for the suggestion!
> Sascha

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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